Connection element for ignition cables having a tubular internal conductor



Nov. 5, 1963 3,109,691

BURKHARDT H. CONNECTION ELEMENT FOR IGNITION CABLES HAVING A TUBULAR INTERNAL CONDUCTOR Filed April 14, 1961 7%W/Kw United States Patent CONNECTION ELEMENT FOR IGNITION CABLES HAVING A TUBULAR INTERNAL CONDUCTQR Hermann Burkhardt, Reutlingen-Betzingen, Germany,

assignor to Richard Hirschmann Radiotechmsches Werk, Esslingen (Neckar), Germany, a firm Filed Apr. 14, 1961, Ser. No. 103,010 Claims priority, application Germany Apr. 21, 1960 4 Claims. (Cl. 339-100) The invention relates to a connection element for ignition cables having a tubular internal conductor.

In order to prevent the ignition systems of motor vehicles from emitting radiation, which disturbs radio and television reception, it is known to interpose resistances of a few kilohrns in the ignition cable at points close to the spark plugs and distributor. In order to save such resistances, ignition cables were developed in which the internal conductors themselves possessed a very high resistance. A section of such a cable which, for use in motor vehicles, has the usual length of the connecting conduits from the distributor to the spark plugs, namely about one-half meter, has the required resistance of a few kilohrns. A suitable construction for such cables comprises a heavy-walled resilient insulating cover and an internal conductor in the form of a tube which is made of a synthetic resin containing a carbon filler. With this type of cable, it is very difiicult to efficiently secure a connector or socket thereon for making separable conductive connections, for example with the spark plugs or the distributors. Since the aforesaid internal conductor cannot be brazed, only a clamp connection can be applied. However, it is necessary to clamp the internal conductor over a relatively wide area against the connector element because in the case of only small-surface contacts the conducting carbon layer becomes thermally overloaded at the contact point due to the extremely high transition resistance. This type of cable, therefore, requires special connectors.

:For the usual ignition cables using a copper braid as internal conductor and a heavy-walled insulating cover, it is customary to use connectors that have a pin which can be inserted into the copper braid of the cable. In some of the connectors, this pin is provided with threads so that it can be screwed into the copper braid of the cable. To facilitate the insertion of the pin it is suitably conically tapered to a point at its free end.

It is possible to secure these known ignition cable connectors to ignition cables having a tubular internal condoctor, but the pin that is screwed into the conductive tube does not find a firm hold and the electrical engagement is unreliable.

A greatly improved connection is provided in accordance with the present invention by the use of a pin whose front portion has a diameter slightly larger than the inner diameter of the tubular internal conductor of the cable, so that said front portion can be inserted therein and held in firm electrical engagement by the resilient tension of the internal conductor and the insulating cover.

The rearward portion of the pin according to the present invention has a larger diameter as Well as threads having sharp edges which, when the pin is screwed in, cut through the internal conductor and penetrate the insulating cover.

The front portion of the pin which has a smaller diameter contacts the .internal conductor over a relatively large area, whereas the rearward threaded portion having a larger diameter firmly engages the cable and cannot be separated therefrom even when the cable is severely pulled, for example for yanking the connector from an outlet box or pulling the socket from the stud of a spark plug.

In order to further increase the contacting area between the front portion of the pin and the tubular internal conductor, it is possible to also provide this portion of the pin with a thread that is suitably blunted so that it will only be pressed into the wall of the internal conductor rather than out into it. Such a thread, moreover, facilitates the insertion of the pin since the latter can then be screwed in from the beginning.

'=A thread, which can only be pressed or caused to cut into the internal conductor, is not sufficient to firmly secure the connector to a cable having a tubular internal conductor. When a cable is pulled, the tractive force must be directly transferred from the heavy-walled insulating cover to the connector or socket. The insulating cover and the internal conductor tube are normally extended to a different degree upon being pulled. If the internal conductor is more extensible than the insulating cover, the connector pin would be withdrawn from the insulating cover by the pulling action. -If the internal conductor is less extensible than the insulating cover, it may be torn off when the cable is pulled and the tractive force is transferred through the internal conductor to the connector. In order to eliminate any such detrimental possibilities, the present invention is concerned with means adapted to transfer any pulling action applied to the cable directly from the insulating cover .to the connector. To this end the thread on the rearward portion of the connector pin must have a diameter so wide, and must be so sharp-edged, that it will cut through the internal conductor and then penetrate the insulating cover.

The figures illustrate the various embodiments of the connector element of the present invention.

FIG. 1 shows an ignition cable which has a tubular internal conductor and is provided at both its ends with connector elements made in accordance with the present invention;

FIGS. 2 and 3 show, by way of example, two embodi- :ments of the connector pin of the present invention in an enlarged scale.

According to a particularly advantageous embodiment of the connector element of the invention, the root diameter of both the threads is the same. The advantage of this type of structure is that of simplifying the mass production of the connector element, as explained later in greater detail in the description of an efiicient way of making these elements.

In accordance with a further embodiment of the connector pin, the two threads of the pin are provided in the form of a continuous thread. This greatly facilitates the screwing of the pin into the tubular internal conductor of the cable.

The ignition cable shown in FIG. 1 consists of a strongwalled insulating jacket 1 and a tube 2 having a thin wall serving as internal conductor consisting of a synthetic resin having a carbon filler incorporated therein.

Connector elements are provided at both ends of the cable. They are fastened by means of a pin which is screwed into the internal conductor 2. This pin consists of two parts 3 and 4 having ditferent diameters. The front part of the pin has a blunt-edged thread 5 which can only be pressed into the internal conductor, without cutting into it. To facilitate the introduction of the pin the latter is provided with a point 6. The thicker rearward part 3 of the pin has a sharp-edged thread 7 which completely cuts through the internal conductor 2 and also penetrates the strong-walled insulating jacket 1.

FIG. 3 shows the pin just described in an enlarged scale, whereas FIG. 2 relates to a different embodiment of the pin in which the thread of the front part 4 of the pin having the smaller diameter is dispensed with.

The mass production of the connector element according to the present invention involves first turning a pin on a lathe the surface of which has a contour corresponding to the broken line 17 shown in FIG. 3. The unfinished pin is shown as having two cylindrical parts 3 and 4 of dilferent diameters and a truncated cone portion therebetween. The two threads 5 and 7 can be continuously cut in a single operation. As a result of this, the two threads will have the same root diameter and the different external diameters of the threads 5 and 7 obtained in this manner will continuously lead into one another.

The connector element shown in FIG. 1 comprises a socket 8 which is in electrical engagement with the pin. In this case, according to the embodiment shown in the drawing, the socket 8 and pin 3 and 4 are turned from a single blank and are fitted into an insulating sleeve 9 the enlarged part 10 of which slides onto the spark plug when the socket 8 is fitted over the stud of the plug. A groove is carved into the periphery of socket 8 close to the free end thereof and a slit 11 is cut tangentially inside of the groove so that the socket wall is pierced at parts of its circumference. A hairpin-shaped spring 12 made of round wire having its ends bent inwardly at right angles, is slipped into said groove and slit 1.1. The socket 8 is fitted, in the known manner, over the spark plug and is held thereon by the spring. in making the connector element just described it is possible to omit the insulating body 9.

The insulating body 9, at its cable-engaging end, is approximately of the same length as the pin 3 and 4. However, a free space is left around said pin for the insulating jacket 1 of the ignition cable.

The pin 3 and 4, at the other end of the cable, is provided with a collar 13 onto which is fitted a covering sleeve 14. The latter is fastened by bending over the end portions 15 protruding from collar 13. The covering sleeve 14, which may have longitudinal slits, embraces the insulating jacket 1 of the cable and serves as a connector for insertion into a socket in the distributor of a motor vehicle.

The resilient right angle bends 16 at the free end of covering sleeve 14 ensure a firm engagement and most satisfactory contact of the connector in the socket of the distributor.

While there has been shown and described herein a preferred embodiment of the socket and connector parts of the connection elements including the connector pin of the invention, it will be obvious to those skilled in the art that modifications are possible and therefore such modifications are within the scope of the claims.

I claim:

1. A connection element having a cable comprising a tubular internal conductor surrounded by a heavy-walled resilient insulating cover, connector means for establishing an electrical connection with an implement and a metal pin in firm electrical engagement therewith ininserted into said tubular internal conductor, said pin having front and rear portions which are relatively long with reference to the diameter of the pin the front part of said pin having a diameter that is only slightly larger than the interior diameter of said tubular internal conductor of said cable, so that the front part of said pin when inserted into said internal conductor is firmly grasped by the elastic tension of said internal conductor and said insulating cover, the relatively long rearward part of said pin having a larger outer diameter than said front part and having equally dimensioned sharp-edged threads which cut through said internal conductor and penetrate said insulating cover.

2. A connection element having a cable comprising a tubular internal conductor surrounded by a heavy-walled resilient insulating cover, connector means for establishing an electrical connection with an implement and a metal pin in firm electrical engagement therewith inserted into said tubular internal conductor, said pin having front and rear portions which are relatively long with reference to the diameter of the pin the front part of said pin having an outer diameter only slightly larger than the interior diameter of said tubular internal conductor of said cable, and blunt edged equally dimensioned threads which are pressed into the interior wall of said internal conductor without cutting into it, so that the front part of said pin when inserted into said internal conductor is firmly grasped by the elastic tension of said internal conductor and said insulating cover, the rearward part of said pin having a larger outer diameter than said front part and having sharp-edged threads which cut through said internal conductor :and penetrate said insulating cover.

3. A connection element having a cable comprising a tubular internal conductor surrounded by a heavy-walled resilient insulating cover, connector means for establishing an electrical connection with an implement and a metal pin in firm electrical engagement therewith inserted into said tubular internal conductor, said pin having front and rear portions which are relatively long with reference to the diameter of the pin the front part of said pin having a diameter only slightly larger than the interior diameter of said tubular internal conductor of said cable, and blunt-edged equally dimensioned threads pressed into the interior wall of said internal conductor without cutting into it, so that the front parts of said pin when inserted into said internal conductor is firmly grasped by the elastic tension of said internal conductor and said insulating cover, the rearward part of said pin having a larger outer diameter than said front part and having equally dimensioned sharp-edged threads which cut through said internal conductor and penetrate said insulating cover, said two threads having the same root diameter.

4. A connection element having a cable comprising a tubular internal conductor surrounded by a heavy- -walled resilient insulating cover, connector means for establishing an electrical connection with an implement and a metal pin in firm electrical engagement therewith inserted into said tubular internal conductor, said pin having front and rear portions which are relatively long with reference to the diameter of the pin the front part of said pin having an outer diameter only slightly larger than the interior diameter of said tubular internal conductor of said cable, and having blunt-edged equally dimensioned threads which are pressed into the interior wall of said internal conductor without cutting into it, so that the front part of said pin when inserted into said internal conductor is firmly grasped by the elastic tension of said internal conductor and said insulating cover, the rearward part of said pin having a larger outer diameter than said front part and having equally dimensioned sharp-edged threads which cut through said internal conductor and penetrate said insulating cover, said two threads having the same root diameter and their external diameter being continuously lead into one another.

References Cited in the file of this patent UNITED STATES PATENTS 2,483,428 Peters Oct. 4, 1949 2,633,116 Ingram Mar. 31, 1953 2,719,278 Kernen et a1. Sept. 27, 1955 FOREIGN PATENTS 1,185,675 France Feb. 16, 1959 1,211,165 France Oct. 5, 1957 

1. A CONNECTION ELEMENT HAVING A CABLE COMPRISING A TUBULAR INTERNAL CONDUCTOR SURROUNDED BY A HEAVY-WALLED RESILIENT INSULATING COVER, CONNECTOR MEANS FOR ESTABLISHING AN ELECTRICAL CONNECTION WITH AN IMPLEMENT AND A METAL PIN IN FIRM ELECTRICAL ENGAGEMENT THEREWITH ININSERTED INTO SAID TUBULAR INTERNAL CONDUCTOR, SAID PIN HAVING FRONT AND REAR PORTIONS WHICH ARE RELATIVELY LONG WITH REFERENCE TO THE DIAMETER OF THE PIN THE FRONT PART OF SAID PIN HAVING DIAMETER THAT IS ONLY SLIGHTLY LARGER THAN THE INTERIOR DIAMETER OF SAID TUBULAR INTERNAL CONDUCTOR OF SAID CABLE, SO THAT THE FRONT PART OF SAID PIN WHEN INSERTED INTO SAID INTERNAL CONDUCTOR IS FIRMLY GRASPED BY THE ELASTIC TENSION OF SAID INTERNAL CONDUCTOR AND SAID INSULATING COVER, THE RELATIVELY LONG REARWARD 